The present invention relates to an arrangement for mechanical measurement and for regulation of a pulling force of a tractor.
Arrangements of the above mentioned general type are known in the art. One arrangement for regulating the pulling force in the lower link of a plow mounted on a tractor is disclosed in U.S. Pat. No. 3,812,916. It has a gauge member which is formed as a bending rod supported twice in the tractor housing. Both lower links engage outside of the bearing points with the bending stick. A gauge stick formed as a free support is arranged between both bearing points and is clamped with its one end near one bearing point on the bending gauge, whereas its another freely projecting end detects near the other bearing point the bending of the bending stick. The displacement signal of the gauge stick dependent on the pulling force is transmitted via a mechanical regulating rod to the hydraulic control member for the power lift. The disadvantage of this arrangement is first of all that here to construction of the tractor housing on the through going bending axle must be determined. This arrangement with the bending axle is expensive. In many tractor constructions the space for the throughgoing bending axle is not available and thereby this arrangement cannot be used. The exchange of defective structucal part, particularly of the bending axle and the gauge stick is difficult. Furthermore, during bending of the bending stick friction takes place in the bearing points which leads to a respective hysteresis. It is also disadvantageous that this arrangement with the throughgoing bending stick for mechanical measurements has difficulties to be converted to a non-mechanical measuring processes. In many cases it can also be disadvantageous that here only sum of the lower link forces are determined.
Another arrangement for mechanical measurements and for regulation of the pulling force of a tractor by means of an electro-hydraulic lifting mechanism-regulating device is disclosed in the W 082/02815. Here also the bending axle is supported in the housing twice. The bending of the bending axle is detected by a sensing device, and for this purpose at each end of the bending axle coaxially extending gauge sticks are mounted. They extend through the housing-fixed sleeves and actuate with their free end respective inductively operating displacement pickup. In this manner the arrangement with the throughgoing bending axle can be used for an electro-hydraulic lifting mechanism-regulating device. This arrangement has, however, the disadvantage that the bending axle is very long in the longitudinal direction. Here also the bending axle is accessible with difficulties. It also has friction at its bearing points and therefore the resulting hysteresis. The arrangement is thereby expensive and not resistant to vibrations.